AnnoCPAN is a web interface for the documentation of all the
modules on CPAN, where users can add annotations on the margin of
specific paragraphs throughout the POD.
This is a work in progress. Some of the ideas given here may well
change over time.

When I started working on this project, there were many modules on CPAN that don't have mailing lists or other discussion places. Scattered discussions could happen in various places, or some users could post general comments on cpanratings.perl.org. However, there was no central place where users could help each other by commenting on specific features, uses, gotchas, etc. for all Perl modules. A limitation of sites such as CPANRatings (and to a certain degree other sites that host reviews) is that the comments appear out of the context of the module's documentation, so they are necessarily general unless the comment's author decides to write a long review to establish context. AnnoCPAN intends to fill this gap by allowing users to add public annotations on the margin of the documentation of every module on CPAN.

The idea is not new, of course; MySQL and PHP already have something similar. One difference is that notes in AnnoCPAN belong to specific paragraphs instead of chapters, and they are shown on the margin (or between paragraphs, depending on the style sheet) instead of at the bottom of the page.

The AnnoCPAN site has the documentation for all the CPAN modules, and a database of "notes" that can be added through the web interface. When a user views a module's documentation, the POD is shown as HTML together with the notes. This allows users to write very short notes that fill gaps in the documentation; for example, it might be sufficient to say "warning: this method returns different things in scalar and in list context and the POD doesn't mention it!".

The plan is to make the note database available for download under an open license so that other CPAN sites can choose to show the notes. It might also be possible to create a program to patch the local pods in a user's machine so that the notes appear on perldoc! (Clearly labeled as notes, of course).

A note is identified by the distribution, module, and paragraph number. But what happens when a new version of the module comes out? The notes will also have to take the version number of the distribution into account. But, is it viable to show old notes with the POD of the new version? And where? Paragraph numbers can change.

In most cases, the documentation for the new version of a module is very similar to the last one. If it is a bugfix release, there might not be any changes at all; otherwise functions are typically added but not removed. In cases such as this, it would be a good idea to transfer the old notes to the new version. The paragraph to which the note was originally attached can be compared to the paragraphs in the new version and, if one is similar enough (preferably identical), the note is transferred.

If the system can't figure out where to put the old note, the author or a moderator can move it to a place in the new version if the note still applies. Hopefully some of the good notes will become obsolete once the author of the module decides to update the documentation to address the issues mentioned in the note.

Users are able to edit, move, and delete their own notes. Moderators are be able to move or delete any note.

This test version already has essentially all the documentation found on CPAN, except for occasional difficulties with the non-trivial problem of unpacking and identifying the relevant content in distributions which were packed in many different ways.